The Metallicity of the Red Giant Branch in the Disk of NGC 6822

Abstract

Deep J, H, and K' images obtained with the Canada-France-Hawaii Telescope adaptive optics system are used to investigate the metallicity of red giant branch (RGB) stars in three fields in the disk of the Local Group dwarf irregular galaxy NGC 6822. The slope of the RGB on the (K, J-K) color-magnitude diagrams indicates that = -1.0 +/- 0.3. The locus of the RGB is bluer than that of globular clusters with the same RGB slope, by an amount that is consistent with the majority of RGB stars in these fields having an age near 3 Gyr. It is demonstrated that if RGB stars in NGC 6822 are this young then the metallicity computed from the RGB slope may be ~ 0.05 dex too low.Comment: 19 pages of text; 10 figures; to appear in the PAS